The present invention generally relates to selection, manipulation and analysis of nanometer-sized structures. The invention particularly relates to nanotweezer systems and devices.
A brief overview of current techniques and tools relating to optical trapping and manipulation of nanometer-sized (nanoscale) structures are described in an article titled “Optical trapping and manipulation of nanostructures” by Onofrio M. Marago et al. published online in Nature Nanotechnology, Volume 8, November 2013, the contents of which are incorporated herein by reference in their entirety. As used herein, the terms nanometer-sized structures and nanoscale structures (also referred to as nanostructures) will be used to denote materials having at least one dimension of less than one micrometer.
Plasmonic nanoantennas (which may be but are not required to be nanostructures) capable of producing highly localized and intensified electromagnetic fields are at the core of very active research directed towards the efficient trapping of nanoscale objects and their manipulation, which as yet has not been resolved with conventional diffraction-limited optical tweezers (nanotweezers) adapted to trap nanoscale particles (nanoparticles). As such, there is ongoing research for methods of delivering a single suspended nanoscale particle towards a given addressable plasmonic nanoantenna with the intension of trapping the particle by optical gradient forces.
There are two fundamental approaches conventionally employed for the trapping of particles with nanoantennas. The first approach involves illuminating periodic arrays of closely-spaced nanoantennas. In this approach, collective heating from the nanoantennas produces strong fluid convection and thermophoresis that exerts drag forces on the particles. Despite a relatively fast fluid motion (for example, up to 1 μm/s), this technique suffers from the issue of particle agglomeration, which prevents plasmonic trapping of individual particles at a given hotspot. The second approach involves the illumination of a single nanoantenna. Here, collective heating is absent, and the temperature is localized at the illuminated nanoantenna. As a result, the thermoplasmonic convection is extremely weak (<10 nm/s), and the trapping force is primarily provided by the optical gradient force of the nanoantenna. The motion of the suspended particles becomes diffusion-limited and only particles in close proximity to the nanoantenna can be effectively trapped. This can be a very slow process that may take several hours depending on how dilute the fluid medium is. In this manner, individual nanoparticles can be addressed at the cost of a reduced control over the motion of the suspended particles.
The two approaches described above are limited in that they individually result in high concentration or low speed of delivery of the particles. Consequently, neither approach provides a solution for rapid delivery of individual particles to addressable plasmonic hotspots.
With respect to positioning particles in the vicinity of hotspots, one particular conventional technique involves using a tip of an atomic force microscope (AFM) to physically pick up, move, and drop a particle at the hotspot. This AFM pick and place procedure is very complicated and requires expensive instrumentation.
In view of the above, it can be appreciated that there are certain problems, shortcomings or disadvantages associated with the prior art, and that it would be desirable if methods and systems were available for rapid delivery of individual particles to specifically addressable plasmonic hotspots on-demand and achieve high resolution trapping of such particles without persistent perturbing convection and thermophoretic forces.